Results from inverting ERS-1 SAR image mode data into directional ocean wave spectra

Results from validating the ocean wave spectra derived from ERS-1 SAR image mode data are presented. The wave spectra are obtained by combining numerical wave model data with SAR data in an inversion process. The validation is performed using in-situ reference data provided by directional and non-directional wave buoys. A variety of sea-states are considered including a hurricane with significant waveheight around 9 m. Significant wave height, peak wave direction and length are extracted from the in-situ and the SAR derived wave spectra, and compared with each other. Best agreement is observed for the peak wavelength. The large deviation in peak wave direction observed in some cases for the wind modes are explained by the limited along track resolution of the SAR instrument. The observed deviations in significant waveheight (at most 40%) are explained by an imperfect RAR modulation transfer function. However, in most cases the agreement is good as can be seen from the graphical presentation